| Message ID | 20210713220957.3493520-5-dmatlack@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM: x86/mmu: Fast page fault support for the TDP MMU | expand |
On Tue, Jul 13, 2021 at 3:10 PM David Matlack <dmatlack@google.com> wrote: > > Make fast_page_fault interoperate with the TDP MMU by leveraging > walk_shadow_page_lockless_{begin,end} to acquire the RCU read lock and > introducing a new helper function kvm_tdp_mmu_fast_pf_get_last_sptep to > grab the lowest level sptep. > > Suggested-by: Ben Gardon <bgardon@google.com> > Signed-off-by: David Matlack <dmatlack@google.com> Reviewed-by: Ben Gardon <bgardon@google.com> > --- > arch/x86/kvm/mmu/mmu.c | 50 ++++++++++++++++++++++++++++---------- > arch/x86/kvm/mmu/tdp_mmu.c | 41 +++++++++++++++++++++++++++++++ > arch/x86/kvm/mmu/tdp_mmu.h | 2 ++ > 3 files changed, 80 insertions(+), 13 deletions(-) > > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c > index e3d99853b962..dedde4105adb 100644 > --- a/arch/x86/kvm/mmu/mmu.c > +++ b/arch/x86/kvm/mmu/mmu.c > @@ -3105,15 +3105,41 @@ static bool is_access_allowed(u32 fault_err_code, u64 spte) > return spte & PT_PRESENT_MASK; > } > > +/* > + * Returns the last level spte pointer of the shadow page walk for the given > + * gpa, and sets *spte to the spte value. This spte may be non-preset. If no > + * walk could be performed, returns NULL and *spte does not contain valid data. > + * > + * Contract: > + * - Must be called between walk_shadow_page_lockless_{begin,end}. > + * - The returned sptep must not be used after walk_shadow_page_lockless_end. > + */ > +static u64 *fast_pf_get_last_sptep(struct kvm_vcpu *vcpu, gpa_t gpa, u64 *spte) > +{ > + struct kvm_shadow_walk_iterator iterator; > + u64 old_spte; > + u64 *sptep = NULL; > + > + for_each_shadow_entry_lockless(vcpu, gpa, iterator, old_spte) { > + sptep = iterator.sptep; > + *spte = old_spte; > + > + if (!is_shadow_present_pte(old_spte)) > + break; > + } > + > + return sptep; > +} > + > /* > * Returns one of RET_PF_INVALID, RET_PF_FIXED or RET_PF_SPURIOUS. > */ > static int fast_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code) > { > - struct kvm_shadow_walk_iterator iterator; > struct kvm_mmu_page *sp; > int ret = RET_PF_INVALID; > u64 spte = 0ull; > + u64 *sptep = NULL; > uint retry_count = 0; > > if (!page_fault_can_be_fast(error_code)) > @@ -3124,14 +3150,15 @@ static int fast_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code) > do { > u64 new_spte; > > - for_each_shadow_entry_lockless(vcpu, gpa, iterator, spte) > - if (!is_shadow_present_pte(spte)) > - break; > + if (is_tdp_mmu(vcpu->arch.mmu)) > + sptep = kvm_tdp_mmu_fast_pf_get_last_sptep(vcpu, gpa, &spte); > + else > + sptep = fast_pf_get_last_sptep(vcpu, gpa, &spte); > > if (!is_shadow_present_pte(spte)) > break; > > - sp = sptep_to_sp(iterator.sptep); > + sp = sptep_to_sp(sptep); > if (!is_last_spte(spte, sp->role.level)) > break; > > @@ -3189,8 +3216,7 @@ static int fast_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code) > * since the gfn is not stable for indirect shadow page. See > * Documentation/virt/kvm/locking.rst to get more detail. > */ > - if (fast_pf_fix_direct_spte(vcpu, sp, iterator.sptep, spte, > - new_spte)) { > + if (fast_pf_fix_direct_spte(vcpu, sp, sptep, spte, new_spte)) { > ret = RET_PF_FIXED; > break; > } > @@ -3203,7 +3229,7 @@ static int fast_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code) > > } while (true); > > - trace_fast_page_fault(vcpu, gpa, error_code, iterator.sptep, spte, ret); > + trace_fast_page_fault(vcpu, gpa, error_code, sptep, spte, ret); > walk_shadow_page_lockless_end(vcpu); > > return ret; > @@ -3838,11 +3864,9 @@ static int direct_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code, > if (page_fault_handle_page_track(vcpu, error_code, gfn)) > return RET_PF_EMULATE; > > - if (!is_tdp_mmu_fault) { > - r = fast_page_fault(vcpu, gpa, error_code); > - if (r != RET_PF_INVALID) > - return r; > - } > + r = fast_page_fault(vcpu, gpa, error_code); > + if (r != RET_PF_INVALID) > + return r; > > r = mmu_topup_memory_caches(vcpu, false); > if (r) > diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c > index 98ffd1ba556e..313999c462d1 100644 > --- a/arch/x86/kvm/mmu/tdp_mmu.c > +++ b/arch/x86/kvm/mmu/tdp_mmu.c > @@ -527,6 +527,10 @@ static inline bool tdp_mmu_set_spte_atomic_no_dirty_log(struct kvm *kvm, > if (is_removed_spte(iter->old_spte)) > return false; > > + /* > + * Note, fast_pf_fix_direct_spte() can also modify TDP MMU SPTEs and > + * does not hold the mmu_lock. > + */ > if (cmpxchg64(rcu_dereference(iter->sptep), iter->old_spte, > new_spte) != iter->old_spte) > return false; > @@ -1536,3 +1540,40 @@ int kvm_tdp_mmu_get_walk(struct kvm_vcpu *vcpu, u64 addr, u64 *sptes, > > return leaf; > } > + > +/* > + * Returns the last level spte pointer of the shadow page walk for the given > + * gpa, and sets *spte to the spte value. This spte may be non-preset. If no > + * walk could be performed, returns NULL and *spte does not contain valid data. > + * > + * Contract: > + * - Must be called between kvm_tdp_mmu_walk_lockless_{begin,end}. > + * - The returned sptep must not be used after kvm_tdp_mmu_walk_lockless_end. > + * > + * WARNING: This function is only intended to be called during fast_page_fault. Heh, this warning seems a bit overkill, but no harm there. > + */ > +u64 *kvm_tdp_mmu_fast_pf_get_last_sptep(struct kvm_vcpu *vcpu, u64 addr, > + u64 *spte) > +{ > + struct tdp_iter iter; > + struct kvm_mmu *mmu = vcpu->arch.mmu; > + gfn_t gfn = addr >> PAGE_SHIFT; > + tdp_ptep_t sptep = NULL; > + > + tdp_mmu_for_each_pte(iter, mmu, gfn, gfn + 1) { > + *spte = iter.old_spte; > + sptep = iter.sptep; > + } > + > + /* > + * Perform the rcu_dereference to get the raw spte pointer value since > + * we are passing it up to fast_page_fault, which is shared with the > + * legacy MMU and thus does not retain the TDP MMU-specific __rcu > + * annotation. > + * > + * This is safe since fast_page_fault obeys the contracts of this > + * function as well as all TDP MMU contracts around modifying SPTEs > + * outside of mmu_lock. > + */ > + return rcu_dereference(sptep); > +} > diff --git a/arch/x86/kvm/mmu/tdp_mmu.h b/arch/x86/kvm/mmu/tdp_mmu.h > index 93e1bf5089c4..361b47f98cc5 100644 > --- a/arch/x86/kvm/mmu/tdp_mmu.h > +++ b/arch/x86/kvm/mmu/tdp_mmu.h > @@ -89,6 +89,8 @@ static inline void kvm_tdp_mmu_walk_lockless_end(void) > > int kvm_tdp_mmu_get_walk(struct kvm_vcpu *vcpu, u64 addr, u64 *sptes, > int *root_level); > +u64 *kvm_tdp_mmu_fast_pf_get_last_sptep(struct kvm_vcpu *vcpu, u64 addr, > + u64 *spte); > > #ifdef CONFIG_X86_64 > bool kvm_mmu_init_tdp_mmu(struct kvm *kvm); > -- > 2.32.0.93.g670b81a890-goog >
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index e3d99853b962..dedde4105adb 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -3105,15 +3105,41 @@ static bool is_access_allowed(u32 fault_err_code, u64 spte) return spte & PT_PRESENT_MASK; } +/* + * Returns the last level spte pointer of the shadow page walk for the given + * gpa, and sets *spte to the spte value. This spte may be non-preset. If no + * walk could be performed, returns NULL and *spte does not contain valid data. + * + * Contract: + * - Must be called between walk_shadow_page_lockless_{begin,end}. + * - The returned sptep must not be used after walk_shadow_page_lockless_end. + */ +static u64 *fast_pf_get_last_sptep(struct kvm_vcpu *vcpu, gpa_t gpa, u64 *spte) +{ + struct kvm_shadow_walk_iterator iterator; + u64 old_spte; + u64 *sptep = NULL; + + for_each_shadow_entry_lockless(vcpu, gpa, iterator, old_spte) { + sptep = iterator.sptep; + *spte = old_spte; + + if (!is_shadow_present_pte(old_spte)) + break; + } + + return sptep; +} + /* * Returns one of RET_PF_INVALID, RET_PF_FIXED or RET_PF_SPURIOUS. */ static int fast_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code) { - struct kvm_shadow_walk_iterator iterator; struct kvm_mmu_page *sp; int ret = RET_PF_INVALID; u64 spte = 0ull; + u64 *sptep = NULL; uint retry_count = 0; if (!page_fault_can_be_fast(error_code)) @@ -3124,14 +3150,15 @@ static int fast_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code) do { u64 new_spte; - for_each_shadow_entry_lockless(vcpu, gpa, iterator, spte) - if (!is_shadow_present_pte(spte)) - break; + if (is_tdp_mmu(vcpu->arch.mmu)) + sptep = kvm_tdp_mmu_fast_pf_get_last_sptep(vcpu, gpa, &spte); + else + sptep = fast_pf_get_last_sptep(vcpu, gpa, &spte); if (!is_shadow_present_pte(spte)) break; - sp = sptep_to_sp(iterator.sptep); + sp = sptep_to_sp(sptep); if (!is_last_spte(spte, sp->role.level)) break; @@ -3189,8 +3216,7 @@ static int fast_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code) * since the gfn is not stable for indirect shadow page. See * Documentation/virt/kvm/locking.rst to get more detail. */ - if (fast_pf_fix_direct_spte(vcpu, sp, iterator.sptep, spte, - new_spte)) { + if (fast_pf_fix_direct_spte(vcpu, sp, sptep, spte, new_spte)) { ret = RET_PF_FIXED; break; } @@ -3203,7 +3229,7 @@ static int fast_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code) } while (true); - trace_fast_page_fault(vcpu, gpa, error_code, iterator.sptep, spte, ret); + trace_fast_page_fault(vcpu, gpa, error_code, sptep, spte, ret); walk_shadow_page_lockless_end(vcpu); return ret; @@ -3838,11 +3864,9 @@ static int direct_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code, if (page_fault_handle_page_track(vcpu, error_code, gfn)) return RET_PF_EMULATE; - if (!is_tdp_mmu_fault) { - r = fast_page_fault(vcpu, gpa, error_code); - if (r != RET_PF_INVALID) - return r; - } + r = fast_page_fault(vcpu, gpa, error_code); + if (r != RET_PF_INVALID) + return r; r = mmu_topup_memory_caches(vcpu, false); if (r) diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c index 98ffd1ba556e..313999c462d1 100644 --- a/arch/x86/kvm/mmu/tdp_mmu.c +++ b/arch/x86/kvm/mmu/tdp_mmu.c @@ -527,6 +527,10 @@ static inline bool tdp_mmu_set_spte_atomic_no_dirty_log(struct kvm *kvm, if (is_removed_spte(iter->old_spte)) return false; + /* + * Note, fast_pf_fix_direct_spte() can also modify TDP MMU SPTEs and + * does not hold the mmu_lock. + */ if (cmpxchg64(rcu_dereference(iter->sptep), iter->old_spte, new_spte) != iter->old_spte) return false; @@ -1536,3 +1540,40 @@ int kvm_tdp_mmu_get_walk(struct kvm_vcpu *vcpu, u64 addr, u64 *sptes, return leaf; } + +/* + * Returns the last level spte pointer of the shadow page walk for the given + * gpa, and sets *spte to the spte value. This spte may be non-preset. If no + * walk could be performed, returns NULL and *spte does not contain valid data. + * + * Contract: + * - Must be called between kvm_tdp_mmu_walk_lockless_{begin,end}. + * - The returned sptep must not be used after kvm_tdp_mmu_walk_lockless_end. + * + * WARNING: This function is only intended to be called during fast_page_fault. + */ +u64 *kvm_tdp_mmu_fast_pf_get_last_sptep(struct kvm_vcpu *vcpu, u64 addr, + u64 *spte) +{ + struct tdp_iter iter; + struct kvm_mmu *mmu = vcpu->arch.mmu; + gfn_t gfn = addr >> PAGE_SHIFT; + tdp_ptep_t sptep = NULL; + + tdp_mmu_for_each_pte(iter, mmu, gfn, gfn + 1) { + *spte = iter.old_spte; + sptep = iter.sptep; + } + + /* + * Perform the rcu_dereference to get the raw spte pointer value since + * we are passing it up to fast_page_fault, which is shared with the + * legacy MMU and thus does not retain the TDP MMU-specific __rcu + * annotation. + * + * This is safe since fast_page_fault obeys the contracts of this + * function as well as all TDP MMU contracts around modifying SPTEs + * outside of mmu_lock. + */ + return rcu_dereference(sptep); +} diff --git a/arch/x86/kvm/mmu/tdp_mmu.h b/arch/x86/kvm/mmu/tdp_mmu.h index 93e1bf5089c4..361b47f98cc5 100644 --- a/arch/x86/kvm/mmu/tdp_mmu.h +++ b/arch/x86/kvm/mmu/tdp_mmu.h @@ -89,6 +89,8 @@ static inline void kvm_tdp_mmu_walk_lockless_end(void) int kvm_tdp_mmu_get_walk(struct kvm_vcpu *vcpu, u64 addr, u64 *sptes, int *root_level); +u64 *kvm_tdp_mmu_fast_pf_get_last_sptep(struct kvm_vcpu *vcpu, u64 addr, + u64 *spte); #ifdef CONFIG_X86_64 bool kvm_mmu_init_tdp_mmu(struct kvm *kvm);
Make fast_page_fault interoperate with the TDP MMU by leveraging walk_shadow_page_lockless_{begin,end} to acquire the RCU read lock and introducing a new helper function kvm_tdp_mmu_fast_pf_get_last_sptep to grab the lowest level sptep. Suggested-by: Ben Gardon <bgardon@google.com> Signed-off-by: David Matlack <dmatlack@google.com> --- arch/x86/kvm/mmu/mmu.c | 50 ++++++++++++++++++++++++++++---------- arch/x86/kvm/mmu/tdp_mmu.c | 41 +++++++++++++++++++++++++++++++ arch/x86/kvm/mmu/tdp_mmu.h | 2 ++ 3 files changed, 80 insertions(+), 13 deletions(-)